naysayer vs thwarter

naysayer and thwarter both are nouns.

Word	Noun	Adjective	Verb	Adverb
naysayer	Yes	No	No	No
thwarter	Yes	No	No	No

As nouns, thwarter is a hypernym of naysayer; that is, thwarter is a word with a broader meaning than naysayer:

naysayer: someone with an aggressively negative attitude
thwarter: someone who systematically obstructs some action that others want to take

Other hypernyms of naysayer include obstructer, obstructionist, obstructor, resister.

naysayer (noun)	thwarter (noun)
someone with an aggressively negative attitude	someone who systematically obstructs some action that others want to take